This invention relates generally to overload relays utilized in motor control centers and more particularly to a reset mechanism for overload relays in a motor starter assembly within a motor control center.
A motor control center provides for grouping of electrical motor control and other related devices in a compact, free-standing installation. Common components within a motor control center include a motor starter, which requires some form of overcurrent protection. Fuses and/or overload relays are commonly provided with the starters for overcurrent protection. Overload relays are electrical switches typically employed in industrial settings to protect electrical equipment from damage due to overheating in turn caused by excessive current flow.
In a conventional setup, an overload relay is connected in series with a control switch. When an overload condition is detected by the relay, the same cuts off power to the coil of the relay allowing the relay to open and disconnect the electrical equipment that is controlled by the relay from the source of power to prevent damage to the electrical equipment.
In a typical case, an overload relay, once tripped, will remain in an open position thereby preventing current flow. Consequently, in order to resume operation of the equipment being controlled by the system, the overload relay must be reset and this is typically accomplished manually. Usually, a push button is employed so that the person operating the equipment may push the push button to cause a reset of the system, causing the overload relay to again allow current to flow to the electrical equipment.
Traditionally, the prior art has provided reset extension arms that are mounted to the enclosure door with a connection between the door mounted reset button and the reset buttons on the overload relays. Thereby the overload relay may be reset merely by depressing the button without the necessity of opening the enclosure door.
U.S. Pat. No. 4,051,340 discloses an overload relay reset assembly comprising a reset rod and an extension rod. The extension rod is detachably mounted to the reset rod, wherein the extension rod extends from the reset rod to an access door of a metal enclosure containing the overload relay.
U.S. Pat. No. 4,011,423 discloses a common reset extension for a plurality of overload relays. A reset extension is provided for resetting all relays simultaneously by depressing a single reset button mounted on the cover of an enclosure, which houses the relays. The reset extension contains pockets for receipt of the relay reset handles, which are biased in a forward direction by a spring and can be manually depressed in a rearward direction.
U.S. Pat. No. 4,005,615 discloses a reset mechanism for an overload relay which is manually operable from the exterior of a explosion proof threaded enclosure. The reset mechanism includes a handle rotatably mounted on the exterior of the enclosure, a connecting rod having one end mechanically coupled to the handle and positioned within the enclosure for reciprocal movement between an initial position and a reset position, and an actuating member mechanically coupled to the other end of the rod and having the ability to engage and depress the reset button when the rod is moved by the handle to a reset position.
Use of prior art mechanisms, such as a T-bar attached to a door mounted manual reset button""s extension arm, allow for possible access to a plurality of overload relay reset buttons when no obstruction exists in the motor control center for door opening-closing and travel of the door""s manual reset button""s extension arm. However, the prior art fails to appreciate the problem of using a single manual reset button and extension arm to reset a plurality of overload relays when at least one of a plurality of overload relays is obstructed.
An electromechanical solenoid-type reset device may also be used to reset an overload relay. These solenoids are electrically wired out to a push-button contact on the motor control center door. In applications where there are a plurality of overload relays, each relay will require a separate solenoid for the purpose of resetting the relay. The requirement of multiple solenoids increases the cost of the motor control center and, therefore, is not an economical solution.
In order to overcome the above noted disadvantage of the prior art, the present invention provides for a single point-to-two point overload relay reset mechanism. The single point-to-two point overload relay reset mechanism provides a low-cost solution for accessing a plurality of overload relay reset buttons in a motor control center with the use of a single door mounted manual reset button and extension arm.
It is the principal object of the present invention to provide a new and improved reset mechanism for an overload relay. More particularly, it is an object of the present invention to provide such a mechanism that will reset a plurality of overload relays within a motor starter located in a motor control center. A single point-to-two point overload reset mechanism allows for the use of a single manual door reset button and extension arm to depress the single point-to-two point overload reset mechanism, which in turn depresses a plurality of overload relay reset buttons. Following contact with the overload relay reset buttons, the single point-to-two point overload reset mechanism returns to a non-contact position with respect to the overload relay reset buttons.
Examples of the more important features of the invention thus have been summarized rather broadly in order that the detailed description thereof that follows may better be understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto.